Fleshing it out a little

lib/index.js

-//const path = require("path");
-
 "use strict";
 
+var path = require("path");
+var worker = require(path.join(__dirname, "worker.js"));
+
 function factory(arg) {
-	var fn = typeof arg === "function";
+	var fn = typeof arg === "function",
+	    obj = undefined;
+
+	obj = worker(arg, fn);
 
-	return fn;
+	return obj;
 }
 
 module.exports = factory;

lib/worker.js

+"use strict";
+
+var spawn = require("child_process").spawn;
+
+function factory(arg) {
+	var ps = spawn("grep", [arg]);
+
+	ps.on("close", function (code, signal) {
+		console.log("child process terminated due to receipt of signal " + signal);
+	});
+
+	return ps;
+}
+
+module.exports = factory;

src/index.js

-//const path = require("path");
+const path = require("path");
+const worker = require(path.join(__dirname, "worker.js"));
 
 function factory (arg) {
-	let fn = typeof arg === "function";
+	let fn = typeof arg === "function",
+		obj;
 
-	return fn;
+	obj = worker(arg, fn);
+
+	return obj;
 }
 
 module.exports = factory;

src/worker.js

+const spawn = require("child_process").spawn;
+
+function factory (arg) {
+	let ps = spawn("grep", [arg]);
+
+	ps.on("close", function (code, signal) {
+		console.log("child process terminated due to receipt of signal " + signal);
+	});
+
+	return ps;
+}
+
+module.exports = factory;